How can i buy a set of IP addresses so that i can keep them for myself forever.I am working with application server which requires static IPs for a very long period of time.I know about DNS but am not willing to go with it.

should i be buying the IPs from the ISP directly?
Can i buy the IPs and set it up with any ISP i want to?

TQ

EDIT:
I want about 100 IPs

How many IPs do you need (and you also need to know how much money can be allocated)? IPs are routing information, the smallest block of IPs that can be separate unit (and so it can be untied from ISP) is /24 (that means, 2^8 adresses out of 2^32 sharing first 24 bits). Also you will need to properly organize routing, which is not as trivial as with just ISP-managed block. IPs are gradually becoming scarce resource (depends on where you live, though). If you need a smaller block, it will always be routed through ISP, so you will never be able to separate it from the ISP. Actually, IPs are not exactly sold, they are only allocated by local network regulation organizations, so in a few years' timescale you cannot be absolutely sure that your address will not suffer, say, renumbering, or worse..